1. Field of the Invention
The present invention relates to a zoom lens system having a zoom ratio of approximately 3, for a small video camera or a digital camera, etc.
2. Description of the Related Art
There has been a need for the miniaturization of video cameras, digital cameras, etc. In order to meet this need, it is necessary to reduce either the length of the entire zoom lens, or the diameter of the front lens.
A retrofocus type small zoom lens is known having two lens groups consisting of a first lens group having a negative power and a second lens group having a positive power, arranged in this order from the object side.
However, in this known retrofocus type zoom lens having two lens groups, since zooming is carried out only by utilizing the second lens group as a master lens, it is difficult to increase the zoom ratio. Moreover, if the F-number is reduced (aperture is increased) in the retrofocus type zoom lens, the diameter of the rear lens group is increased and high-order spherical aberrations are produced.
A four-lens group type zoom lens is also known having a positive first lens group, a negative second lens group (variator), a negative third lens group (compensator), and a positive fourth lens group (master lens), arranged in this order from the object side. However, in this type of zoom lens, since zooming is effected chiefly by utilizing the second lens group as a variator, the length of the whole lens system is increased, the diameter of the frontmost lens is increased, and, it is difficult to increase the angle of view.